1. Field of the Invention
The present invention relates to an optical writing device for exposing a surface of an exposure object to light by a plurality of light emitting elements. The present invention also relates to an electrophotographic image forming apparatus.
2. Description of the Related Art
Among electrophotographic image forming apparatuses, a typical image forming apparatus for business use generally utilizes, as an exposure device, an optical writing device which includes light emitting elements, such as LEDs or Els, aligned in an array for downsizing, noise reduction, and power saving.
The use of such an optical writing device provided with light emitting elements aligned in an array can shorten the light path of the optical system to make the device compact and can eliminate a rotating mechanism for noise reduction.
However, an optical writing device for A3 width with a resolution of 600 dpi for example has as many as about 7,000 light emitting elements arranged in one line and hence is constructed to guide light rays emitted from the respective light emitting elements to a photosensitive member through a lens array of selfoc lenses for example. Therefore, the light path is extremely short so that the depth of focus is shallow, which causes a disadvantage that focal shift is likely to occur.
Some of conventional image forming apparatuses have a countermeasure against such focal shift to realize accurate focusing. For example, an image forming apparatus disclosed in Japan Patent Laid-open Publication No. H5-278266 is provided with an adjustment mechanism for adjusting the distance between an optical writing head and a photosensitive member. In this image forming apparatus, the distance between the optical writing head and the photosensitive member is adjusted to provide the sharpest focus by manipulating the adjustment mechanism utilizing a jig inserted in the image forming apparatus or by manipulating the adjustment mechanism while monitoring the results of image forming processing actually performed.
However, the prior art technique described above is based on the premise that the space for mounting a support unit for positioning the writing head relative to the image carrier is defined properly in the image forming apparatus.
For this reason, even if the positioning of the writing head is made before the mounting thereof to the image forming apparatus, the entire support unit as mounted to the image forming apparatus may be deformed due to an external force exerted from the image forming apparatus. In such a case, proper positioning of the writing head needs to be made again after the writing head is mounted to the image forming apparatus.
When the support unit is entirely deformed irregularly with the optical writing device in the state mounted to the image forming apparatus, it is extremely difficult to properly adjust the position of the writing head relative to the image carrier. Accordingly, an intended electrostatic latent image cannot be formed on a surface of the image carrier, which hinders proper image forming processing.